Grass Genera of the World

L. Watson and M. J. Dallwitz


Pereilema J. & C. Presl

Habit, vegetative morphology. Annual; caespitose. Culms 30–60 cm high; herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Leaves not basally aggregated; auriculate. Leaf blades narrow; 2–5 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent; an unfringed membrane; 0.5 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile, or hermaphrodite, male-only, and sterile; overtly heteromorphic (in bunches, some of each group bisexual and the rest incomplete or ‘reduced to glumes or bristles’).

Inflorescence. Inflorescence of spicate main branches to a false spike, with spikelets on contracted axes (the spikelet clusters being subsessile on appressed spike-like laterals, which decrease in length towards the tip of the main axis - cf. Sporobolus, apart from the awns); contracted (plumose by the long lemma awns). Primary inflorescence branches 16–25 (or more). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced, or ‘racemes’; disarticulating (P. ciliatum), or persistent; falling entire (the main branches falling, in P. ciliatum). Spikelets with ‘involucres’ of ‘bristles’ (representing reduced spikelets - the ‘involucre’ to one side). The ‘bristles’ deciduous with the spikelets. Spikelets secund (the clusters one-sided).

Female-fertile spikelets. Spikelets morphologically ‘conventional’ (when the spikelet cluster is dissected out); 2 mm long (to 3 cm with the awns); compressed laterally; disarticulating above the glumes (when the inflorescence branches fall entire, the florets also disarticulate). Rachilla terminated by a female-fertile floret. Hairy callus present.

Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; when not reduced to bristles, hairless (the keel scabrid); awned (the awns long, straight, scabrid); carinate; similar (hyaline, emarginate, or sometimes reduced to ciliate bristles in P. ciliatum). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (becoming hardened in the fruit); not deeply cleft; mucronate to awned. Awns 1; median; apical; non-geniculate; hairless (scabrid, slender); usually much longer than the body of the lemma (to 3 cm long); persistent. Lemmas hairless; scabrous; carinate; without a germination flap; 3 nerved. Palea present; relatively long; apically notched; awnless, without apical setae to with apical setae (the nerves slightly excurrent); not indurated (hyaline); 2-nerved; 2-keeled. Lodicules absent. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Pericarp fused. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae several per cell. Long-cells intercostal long-cells very thin-walled. Mid-intercostal long-cells having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (24–)25.5–27(–30) microns long. Microhair basal cells 9–12 microns long. Microhairs 10.5–12 microns wide at the septum. Microhair total length/width at septum 2.1–2.6. Microhair apical cells 6–9 microns long. Microhair apical cell/total length ratio 0.22–0.35. Stomata common; 19–24 microns long. Subsidiaries parallel-sided and dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal silica bodies absent. Prickles abundant. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section. Midrib conspicuous; having a conventional arc of bundles (the large median flanked by a small lateral on each side); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (in addition to large ‘midrib hinges’); associated with colourless mesophyll cells to form deeply-penetrating fans (these incorporated in the wide colourless girders). All the vascular bundles accompanied by sclerenchyma. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10. 2n = 20.

Taxonomy. Chloridoideae; main chloridoid assemblage.

Distribution, ecology, phytogeography. 3 species; Mexico to tropical South America. Species of open habitats. Hills and weedy places in savanna.

Neotropical. Caribbean and Andean.

Rusts and smuts. Rusts — Puccinia.

References, etc. Leaf anatomical: this project.

Special comments. Fruit data wanting.


Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘Grass Genera of the World: Descriptions, Illustrations, Identification, and Information Retrieval; including Synonyms, Morphology, Anatomy, Physiology, Phytochemistry, Cytology, Classification, Pathogens, World and Local Distribution, and References.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).

Index